Tunable squirrel cage magnetron



Nov. 10, 1953 M. D. HARE ETAL 2,659,033

TUNABLE SQUIRREL CAGE MAGNETRON s sheets-Shea 1 Filed March 29, 1946 INVE'NTOR MILTON D. HARE VIRGINIA LEONARD ATTORNEY Y- 1953 M. 0. HARE ETAL 2, 5 ,033

TUNABLE SQUIRREL CAGE MAGNETRON Filed March 29, 1946 3 Sheets-Sheet 2 INVENTOR MILTON D. HARE VIRGINIA LEONARD ATTORNEY Nov. 10, 1953 D HARE ET AL 2,659,033-

TUNABLE SQUIRREL CAGE MAGNETRON I Filed March 29, 1946 3 Sheets-Sheet 3 INVENTOR MILTON D. HARE VIRGINIA LEONARD MAQMQH Q- ATTO R NEY Patented Nov. lQ, 1953 D" ATE 2,6510%? I U B SQ B QAQEMAGNETB N Milton D. Hare, Chicago, Ill., andVirgini'a- Leonard, Arlington, Mass; assign'ors *tdth'e United States of America as. represented by theSecretary of War. @9 t is fiiuwzfihat 7 Claims. (01. 3315-40) This invention rclates'to electrical apparatus and more particularly to tunable magnetronsf One type of tunable magnetron radio frequency oscillator is the so called squirrel cage magnetron. The squirrel cage magnetron is generally constructed as a substantially cylindrical cavity resonator within which is placed an axially aligned cathode structure. Cylindric'ally arranged about this cathode and within the cavity resonator is a ring of interleaving anode fingers. Adjacent fingers in this ring are'connected atone end thereof to one of two opposite annular anode halves, the anode halves in turn being connected to the opposite end closures of the cavity resonator. A magnetic field is maintained'parallel to the magnetron axis by means of two magnetic pole pieces. The anode halves may be provided with water cooling coils to assist in heat dissipation. The term squirrel cage. is derived from the appearance of the cylindrical ring formed by the two sets of interleaving anode fingers. Tunmg of the magnetron is effected by making at least one of the'cavity resonator end closures flexible so that it may be moved with respect to the opposite end closure. This relative motion resultsin a relative axial motion of the interleaving anode fingers with respect to each other thereby varying the frequency of the magnetron.

The present invention is concerned primarily with the standardization and simplification of themanufacturing procedure for squirrel cage magnetrons; Formerly the construction was comparatively diificult because of the many close machining tolerances, the necessity for careful alignment of the various magnetron components and'the difiiculty of maintaining the alignment during the soldering processing. It is desirable to'red'uce the number of close tolerances in the machining, to allow the magnetron components to'be drawn from sheet stock as far as possible, to simplify the alignment of the'magnetron components and to simplify the assembly and soldering of the magnetron.

Accordingly an object of the present invention is to simplify the. assembly and the construction of squirrel cage. magnetrons.

' A further object of the present invention is to decrease the expense of manufacture by utilizing die stamping processes instead of machining processes whereever possible.

' A still further object of the present invention isto provide jigs for simplifying'the attainment and maintenance of the critical alignment of the magnetron components in the'assembly process.

2 Other objects and advantages of the; invention will be apparent during-thecourse of the-"icilowing description; f In essence the manufacturing process and-the principal magnetron components may bedescribed by the'fo'ur subassemblieswhich are the anode-cavity assembly; the cathode fpole piece assembly, the output loop assembly and'tn fifin assembly in which the other two assemblies are joined to the anode-cavity assemblyf In the anode-cavity assembly two "jigs are-used; the upper jig holds the "tuner yolgeftlieupper magnetic 'pole" piece and the upperfannul anode half in axial alignment, while 'thelower' holds the cavity resonator sh'ell'an'd lower annular anocle'half in axial alignment. Themwemig also holds the upper and lower annular anode halves in axial alignment with each'etlierthereby aligning the upper ancilowercomponents. The anode cooling coils'are held in'pl'ace by grooves on the outer circumference o fth'e annular anode halves. In 'addition'to' thetwo abovementioned jigs, there is, a'spacing jig "wh"1ch is inserted through the outpufhole'in'thcavity resonator to secure uniiorrn'spacingoi th anode fingers. The cathode-pole piece; assembly-is assembled separately using the cathode; coaxial heater lead and'the lower'inagnetic pole piece. f

The output loop assembly is likewise. assembled Both the cavity-anode assembly and the final assembly are ma e' bysolderingin' a.- 'hydrcgen atmosphere. g u H In the accompanying drawings forming apart of this specification, Fig. l is an isometric view of a. squirrel cage magnetron construction which illustrates one embodiment of the present invention;

Fig. 2A is a cross'sectional View drawn to a slightly enlarged scaleof the output'loo'p assembly of the magnetron of, Fig. 1 i

Fig. 2B is a partially cross'section ed view'drawn to an enlarged 'scale through the axis'o'f the magnet'ron of Fig. 1,

Fig. S'is'an isometric View drawn to a slightly reduced scale of'the jigs and magnetroneo nponents used in the 'cavity anodeassembly'of "the magnetron of Fig. 1,

Fig. 4A is an isometric view oi the components of Fig. 3 assembled preparatory to soldering. Fig. 4B is an illustrative view takenat' the'l'evel of the output hole 635 f Fig. iAsho' ing the p:-

Q sti n e anod fing r'spaci Jay- Fig. 51s across 's'ectlonarvlew'to an en- 3 larged scale through the axis of the cavity-anode assembly of Fig. 4A, showing the disposition of the solder and Fig. 6 illustrates one method of disposing a heating wire around the cavity-anode assembly of Fig. 4A preparatory to soldering the cavityanode assembly.

In Fig. 1 the squirrel cage magnetron is pictured in an inverted position with its base uppermost. The remaining figures show the magnetron in its customary position. In Fig. 1, numeral I designates the magnetron cavity resonator. Numeral I I designates a tuning mechanism which provides relative movement of the end closures of cavity resonator I0. Two anode cooling coils l2 are disposed above and below cavity resonator I0. An output loop assembly I3 is coupled into the interior of the magnetron cavity resonator I0 and serves as the radio frequency output line. Numeral I4 designates the cathode-pole piece assembly, through which passes the coaxial heater lead from a bayonet plug I5 to the cathode structu're within the magnetron cavity resonator ID. The bayonet plug I5 serves as the external connection for the heater and cathode. A pump lead I6 is connected to the interior of cavity resonator 1 B in order to evacuate the magnetron. Two pole piece connections H are adapted to receive the opposite ends of the magnetic field excitation unit, not shown.

Fig. 2A shows a cross sectional view of the output assembly I3 of Fig. 1 drawn to a slightly enlarged scale. A tapered outer conductor 20 V and tapered inner conductor 2| are electrically -connected by a coupling loop 22 within the magnetron cavity resonator I0. The tapered outer conductor 20 may be made by die stamping a .copper disc.

The magnetron vacuum is maintained by a glass seal 23 which is joined to inner Fig. 2B shows a partially cross sectional view "taken. through the axis of Fig. 1 and drawn to "an enlarged scale.

The magnetron structure within cavity resonator III, the tuner mechanism "II' and the cathode-pole piece assembly I4 are shown in some detail. The cavity resonator I0 f is formed by a cavity resonator shell 30 of sub- 's'tan'tially cylindrical construction and continuous with the rigid end closure of the cavity resonator. A circular diaphragm 3 I, not cross sectioned, constitutes the flexible end closure of cavity resonator ID. The cavity shell 30 may be drawn from a sheet, monel disc; the diaphragm 3-l may be die stamped from a sheet monel disc. Within the cavity resofnator In is a squirrel cage or ring of interleaving anode fingers 32 and 33 which are arranged circumferentially about the magnetron axis with substantially uniform spacing between fingers.

Alternate anode fingers 32 at one end thereof are connected to, or integral with, the upper annular anode section 34, while the other anode fingers 33 at one end thereof are connected to, or integral with, the lower annular anode section 35. Thus anode section 34 and anode fingers '32 may be said to constitute the upper anode while anode section 35 and anode fingers 33 may be said to constitute the lower anode. These are the basic squirrel cage anodes. Various improved anode structures, which involve slight modifica- 4 tions of these basic anodes, have been developed to improve the efliciency of the magnetron. The anodes generally may be milled from copper rod.

The annular anode section 34 passes through and is soldered to diaphragm 3|, while annular anode section 35 passes through and is soldered to the rigid end closure portion of cavity resonator shell 30.

The term soldered indicates a process for affixing two or more metallic members with a good electrical connection therebetween. The soldered junction may be intended primarily as a vacuum seal between the metallic members. Silver solder is commonly used in magnetron work. Gold solder is preferable where a vacuum seal soldered junction including nickel-cobalt is to be made. It is to be understood that any equivalent process may be substituted for the solder- .ing, if desired.

A tuner yoke 35 having substantially the same shape and construction as the cavity shell 30 is soldered atop the junction of diaphragm 3| and cavity shell 30, thereby being rigidly fixed with respect to the cavity shell 36. The annular anode sections 34 and 35 are grooved on their outer circumferences to simplify the support of the anode cooling coils I2 in the cavity-anode assembly and in the completed magnetron.

Centrally disposed within the tuner mechanism II is one of the two magnetic pole pieces, the upper or tuner pole piece 31, not cross sectioned. The face of pole piece 3'! projects slightly below the upper edge of the upper annular anode section 34, and is soldered thereto. The upper end of pole piece 31 is threaded. The tuner pole piece 3'1 is movable with respect to a tuning yoke extension 38, the tuning yoke extension 38 being rigidly affixed to tuning yoke 36 by a number of yoke screws 39, not cross sectioned. Hence relative axial motion of the tuner pole piece with respect to the tuning yoke extension 38 results in relative axial motion between the two annular anode sections and their respective anode fingers. The motion of the tuner pole piece 31 is effected by a tuning adjustment nut 40 operating upon the threaded end of tuner pole piece 31 and moving with respect to the yoke extension 38 upon ball bearings M. is maintained by a spring 42 the tension of which may be adjusted by a tension nut 53. Pole piece 31 maintains pressure against spring 42 by means of a stop washer 44. A shim washer d5 limits the upward motion of the tuner pole piece 31 and hence the maximum separation between the anodes. Another shim washer d6 limits the closest approach of'the anode fingers to the bottom of their respective slots and prevents the anode fingers from butting against the opposite anode section and possibly buckling.

The cathode-pole piece assembly It is shown partially cross sectioned. Numeral 41 designates the cathode, not cross sectioned, within which is the heater element, not shown. Two radially enlarged sections 48 on cathode 4'I are employed in the usual fashion to confine the electron beam. A face of the cathode pole piece designated by numeral 49 projects slightly inside anode section 35. Pole piece face 49 is opposite the face of the tuner pole piece 31 so that a magnetic field between the two faces is maintained parallel to the magnetron axis in the usual fashion. The cathode-pole piece assembly I4 is soldered to the annular anode section 35 around the circumference and at the juncture between pole piece face 49 and anode section 35. The'cathode and heater Pressure against pole piece 31 4 cacao-ea meral and is connected by a wire 5m to outer conductor 52 of the coaxial heater lead. Outer terminal 5! and outer conductor 52 arealso the' cathode connection, the cathode being connected t6 one side of the heater. A vacuum seal 53 extends between a nickel cobalt tube 54 and the terminal 5| and serves to insulate terminal 51 from the main metallic surface of the magnetron. The inner and outer terminals of bayonet base l5' are insulated by an insulating bead 55.

glass bead 56 serves to insulate and suppo t inner conductor 50 from outer conductor52, and

also as a vacuum seal.

Fig. 3 shows the several niagnetroncomponents and the jigs used in the cavity-anode assembly.

An upper jig holds the tuning yoke 36,the tuner polepiece 3], and the upper annular anode section 34, in axial alignment. A lower jig 6|, resting in a support 62, holds the cavity'shell 30, the lower annular anode section 35, the diaphragm 3| and the upper annular anode section 34 in axial alignment. This maintains the axial alignment which is necessary for the cavityanode assembly. The jigs 60 and BI may be oxidized stainless steel to prevent their being soldered to the assembly.

The upper and lower anodes are shown isometrically in Fig. 3. Annular anode sections 34 andjfi and theirrespective anode fingers 32 and 33 are the basic squirrel cage anodes.

Various improved. anode structures which involve rearrangements of the anode fingers or special tuningmeans may be used, if desired; Thus for example, the efficiency may be improved by usingphase reversing anode fingers; in one form of .phase reversing finger, the adjacent fingers in two diametrically opposite pairs of fingers are connected to the same anode section, theremamaerer the fingers being rearranged to be alternately connected to opposite anode sections; in another form of phase-reversing fingers, each of the'aforementioned pairs of fingers is replaced by a single wide anod e finger. As further exairiples, various anode structures for extending the tuning range, e misecuring a desired shape of tuning curve, or for decreasing moding of the magnetron, have beendevised. Accordingly the invention is not limited to the anode structure shown.

Referring in Fig. 3 to the drawing of the cavity shell 30, numeral 53 designates an output hole.

Fig. 4A is a simplified isometric view showing the magnetron components for the anode-cavity assembly assembled on the upper and lower jigs 60 and 6|, and supported on the support 62. A spacing tool 64 is inserted in the output hole 63 in order to accurately adjust the spacing between two adjacent anode fingers. The action of this spacing tool is illustrated in Fig. 43.

An illustration of the alignment of the components and the position of the solder prior to soldering the cavity-anode assembly is shown in Fig. 5. As herein described, wire solder, general- 1y silver or gold solder, may be used. However the actual method of making the junctions is not intended to limit the applicability of the invention. Where the solder may be held in position by gravity, as at 65, the wire solder is merely placed around the junction to be soldered. When this cannot be done, as at point 66, the solder is spot welded into place at several points.

' optional and high frequency induction heating as. shews'oiip ssibieinetned of finalising"; a

to serve as a fiux for the solder and to prevent the formation of oxides which is in accordance with standard practice in the vacuumtube industry. The method of heating described is of course or any oth'er method of affixing the parts may be used.

After the completion of the cavity anode assemblv as described above, the remaining components'areattached to the magnetron. Theoutput assembly I3 is assembled separately and the cathode'-pole1:viece'assembly I 4 is likewise assembled separately. These two assemblies maybe attached to the cavity-anode assembly by much the" same procedure as that outlined for soldering the cavity-anode assembly. The tuner assembly II is not a part of the vacuum system and is removable for adjustment. It is attached to the remaining structure after the assembly is com-- pleted. The evacuation and degassing of the magnetron are accomplished in the usual fashion.

The use of the jigs in the assembly and thedesign of the magnetron components result a great simplification of the manufacturing process. Tolerances have been reduced and" practically all of the magnetron components except the anodes require little or no machining, and may be largely formed or die stamped. The practically all-metallic construction of them'agnetr'on is most advantageous. I

I It is obvious that there may be deviations from the invention as described which still fall fairly within the'spirit and scope of the invention. a

) Accordingly all such deviations are claimed which fall fairly within the spirit and scope of the invention as identified in the hereinafter appended claims.

What is claimed is: I v

1. A squirrel cage magnetron including a cylindrical cathod and a substantially cylindrical cavity resonator coaxial" with said cathode, two annular anode sections disposed coaxially with said resonator and connected to Opposite end closures of said resonator, a ring of interleaving anode fingers mounted circumferentially about the axiscf' and within said resonator and entirely between said anode section's, adjacent fingers being connected at one end thereof to opposite annular anode sections, means including magnetic pole pieces at opposite ends of said cavity resonator and each aflixed to one of said anode sections for generating a magnetic field substantially parallel to the axis of said resonator, one of said pole pieces being fixed to said resonator and the other pole piece being adjustably mounted on said resonator and means mounted on said resonator and connected to said other pole piece for moving one of said anode sections and said other pole piece axially with respect to the other anode section and said one pole piece.

2. A squirrel cage magnetron as defined in claim 1 in which one of said end closures of said resonator has a flexible portion, and means connected to said last-named end closure for moving it and its attached fingers axially with respect to the other end closure of said resonator.

3. A squirrel cage magnetron as set forth in claim 1 in which said cavity resonator has a, flexible end closure and in which said means for mov- -ing said anode section and pole piece includes a ble, aring of interleaving anode fingers mounted circumierentially about the axis of and Within said resonator and entirely between said anode sections, adjacent fingers being connected at one end thereof to opposite annular anode sections, means including a pair of magnetic pole pieces at opposite ends of said cavity resonator and each aflixed to one of said anode sections for generating a magnetic field substantially parallel to the axis of said resonator, means mounted on said resonator for moving one of said anode sections and the pole piece aifixed thereto axially with respect to the other anode section and the other pole piece, said last named means including a yoke rigidly affixed to said cavity resonator, the movable pole piece extending axially through said yoke, and means for moving said movable pole piece with respect to said yoke, and anode cooling coils disposed around said circumferential grooves.

5. A magnetron comprising aligned first and second like, hollow, conductive cylinders having open and closed ends, said open ends facing one another, a single circular, flexible conductive diaphragm fastened across said open ends and interconnecting said cylinders, the closed ends of said members and said diaphragm each having a central aperture therein, two opposing annular anode sections disposed concentrically within said cylinders, the first of said sections being mounted within the aperture of said flexible diaphragm and fastened thereto and the second of said sections being mounted within the aperture in the closed end of said first cylinder and fastened thereto, a ring of interleaving anode fingers disposed concentrically within said cylinders, adjacent fingers being connected at one end thereof to opposite annular sections, a cathode disposed concentrically within said ring of fingers, and means connected to said first section for moving said first section axially of said cylinders to effect the tuning of said magnetron.

6. A magnetron as claimed in claim 5, in which said last-named means comprise a third hollow, conductive cylinder concentric with the axis of said first and second cylinders, and of smaller diameter than said first and second cylinders, said third cylinder being without the structure formed by said first and second cylinders and said diaphragm, said third cylinder being mounted at one end thereof to said second cylinder at the closed end thereof, whereby the central aperture in the closed end of said second cylinder is aligned with the hollow portion of said cylinder, a piston within and concentric with said third cylinder fastened at one end to the first of said annular sections, and means connected to said piston for moving said piston axially of said third cylinder.

'7. A magnetron as claimed in claim 6, wherein said piston is formed of ferro-magnetic material, and the end thereof fastened to said first annular section is expanded in the form of a first face plate across the opening in said first annular section, and further including a second face plate of ferro-magnetic material fastened to said second annular anode section across the opening therein, said second face plate including a central aperture therein to allow the passage therethrough of said cathode.

MILTON D. HARE. VIRGINIA LEONARD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,128,237 Dallenbach Aug. 30, 1938 2,259,690 Hansen et al. Oct. 21, 1941 2,284,751 Linder June 2, 1942 2,406,276 White Aug. 20, 1946 2,409,222 Morton Oct. 15, 1946 2,416,899 Brown Mar. 4, 1947 2,419,572 Laico et a1. Apr. 29, 1947 2,424,886 Hansell July 29, 1947 2,428,193 Blewett Sept. 30, 1947 2,500,430 Pierce Mar. 14, 1950 2,505,529 Crawford et al. Apr. 25, 1950 2,524,908 Derby Feb. 20, 1951 FOREIGN PATENTS Number Country Date 509,102 Great Britain July 11. 1939 

